Thoughts on comparing 8-bit and 10-bit footage from the Panasonic GH5

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This video is specifically made to address a confusion many people seem to be having as to why there aren’t any significant differences between the 8-bit and 10-bit footage in the Panasonic GH5, as of March 2017.

I’ve tried to keep it as simple as possible:

You can use the same logic to check for differences in bit depths in other cameras as well.

The takeaway

For 8-bit 4:2:0, shoot 100 Mbps

For 10-bit 4:2:2, shoot 400 Mbps internally, or

For 10-bit 4:2:2, shoot 880 Mbps Prores HQ externally

Calculations and links from the video

The video references a few articles I’ve written earlier; and some calculations that will help you follow my arguments. Here are some preliminary articles that explain the terminology, formulas, etc., mentioned in the video:

Calculations

A full color image (produced by a camera) is a raster image and has three channels – Red, Green and Blue. That’s why we have to multiply the data by 3. If you’re shooting RAW, there’s only one channel, because RAW hasn’t been debayered yet. Once it is, it will also have three channels.

As a separate note, YUV footage also has three channels, one for luminance and two for chrominance. To learn more about this read the following articles:

The traditional way has been to equate interframe and intraframe in this way:

50 Mbps interframe = 100 Mbps intraframe (for 1080p)

4K is four times the data:

200 Mbps interframe = 400 Mbps intraframe (for 4K)

As we saw above, 10-bit 4:2:2 should have a data rate of 280 Mbps in interframe. But the 400 Mbps option will arrive as an intraframe codec. Therefore:

Necessary data rate: 280 Mbps x 2 = 560 Mbps

This is the data rate the GH5 needs in 10-bit 4:2:2 just to be better than 100 Mbps 8-bit 4:2:0. However, the GH5 will only have a 400 Mbps option internally. If you need more, you need to attach an external recorder and record Prores HQ, which has a maximum data rate of 880 Mbps.

Why can we only shoot 400 Mbps internally?

That’s something only Panasonic can definitely answer. Though one reason could be that, internally, you need a V60 class card to write 400 Mbps. V60 stands for 60 MB/s (Class 10 is 10 MB/s).

400 Mbps = 50 MB/s

As you can see, this is just under the maximum spec for V60. That’s probably why the GH5 comes in at 400 Mbps. To have a higher data rate, it needs a better class card (a V90 perhaps, which is 90 MB/s or 720 Mbps). Whether this is doable or not is Panasonic’s call.

As for 150 Mbps in 10-bit, forget it!

It’s not very wise to compare 8-bit and 10-bit in its present form. When the 400 Mbps version comes out, 10-bit will have the room to show if it really is better. Then, it will have no more excuses if it falls short.

Step Four: Color, another angle

You can also think of this in terms of color:

8-bit = 256 shades = 16.7 million colors

10-bit = 1024 shades = 1 billion+ colors

Difference = 1 billion / 16.7 million = 64 times

You’d think you need 64 times the data, but the reality is, the human eye can’t see more than 10 million colors – at best.

Overall though, I don’t think the number of necessary colors (both visual and theoretical) is more than what you get with 880 Mbps Prores HQ, so that’s a great upper limit to go by. If you want the most color juice, use an external recorder. How much of an improvement this is we’ll know once the firmware updates are released.

The takeaway, again

For 8-bit 4:2:0, shoot 100 Mbps

For 10-bit 4:2:2, shoot 400 Mbps internally, or

For 10-bit 4:2:2, shoot 880 Mbps Prores HQ externally

I hope this has helped in your understanding on how bit depth, chroma subsampling and compression works in cameras. What do you think?

Exclusive Bonus: Download my free cheatsheet (with examples) of the most important and useful focal lengths for film and video (PDF file optimized for mobiles and tablets).

Comments

Hey Sareesh thank you very much for this! Reading this site is damn informative and i wish more people talked about these subjects as thruthfully as you do.
I have a question regarding Ext Recorders : do the 880Mbps (Atomos) ProRes already apply or do I have to wait for the firmware update ?

Hi Sareesh,
what is the conclusion about external recorders?
If the signal is compressed and then rescaled what is the benefit of external prores recorder?
Before I read this I thought that there were no compressions on the hdmi signal from the camera and that was just the point – to catch the uncompressed signal from the censor to the recorder.
Ken

i see great benefit in all the examples. the benefit is beeing able to use vlog in camera, which benefits in an extra stop of dynamic range. and it looks good to me, and very usable. this whole heavy compression talk is getting towards pixel peeping. Pro res lt is also too heavy compressed regarding this math, but i doubt anybody here can really tell lt and the normal 422 or hq apart in real life examples.